What should a good welder do well?

For a long time, there has been a view in the field of mechanics that welders are "pure operators", and there are not many opportunities to contact drawings, and the quality requirements for welders are not high. Actually, this is a misunderstanding. An excellent welder should not only have skilled operation skills, but also be able to formulate welding construction scheme, determine welding technology, evaluate product quality, analyze and find out the reasons for unqualified products, so he needs to master the knowledge of many disciplines.

1, mathematics and statistics: when evaluating the weldability of a material, it is necessary to apply relevant formulas to calculate the carbon equivalent, select welding current to test the formula: I=(20~40)d, and calculate the amount of welding material. In addition, you may encounter some problems such as pressure, elongation, fusion ratio and heat input, which are related to mathematical calculation.

According to different materials, different specifications and different welding positions, various suitable process parameters are selected; Welding current, arc voltage, welding material diameter, power polarity, gas flow, welding speed, etc. , involving a lot of data, is a tedious job. An experienced welder can summarize these data statistically; Divide the material for the first time, then divide the welding position for the second time, and then there are various specifications and various process data. It's like making a table and classifying it. Therefore, an experienced welder, facing a weldment, can basically put into work without debugging. Similarly, we should be familiar with and understand the appearance size requirements and quality evaluation standards of various welds.

2. Physics:

2. 1, electrical knowledge:

(1) First of all, we must master the basic knowledge of electricity and use it safely.

(2) Understand the structure of arc; Such as anode region, cathode region and arc column region, electrons move to the anode region at high speed and cations move to the cathode at high speed. The temperature in the anode region is higher than that in the cathode region, and the mass of cations is greater than that of electrons. When DC is reversed, fine particle transition is easy to occur. Therefore, when choosing the polarity of power supply, sometimes it is directly connected and sometimes it is reversely connected.

(3) electromagnetic field knowledge; Understand the reason why the welding cable can't be coiled at work, and take measures to prevent magnetic deviation during welding.

2.2. Master the physical characteristics of some materials, such as strength, hardness, plasticity, toughness, resistivity, thermal conductivity, etc. And take necessary measures for some defects that are easy to appear in welding due to these characteristics. For example, the deformation of stainless steel after welding is larger than that of carbon steel, because the thermal expansion coefficient is 50% larger than that of carbon steel. Cast iron has high hardness and poor toughness. Annealing after welding is to eliminate internal stress and prevent cracking.

2.3, mechanical knowledge:

(1) During welding, the droplet is affected by gravity, arc blowing force, surface tension and extreme pressure. By changing the current, the arc blowing force, the angle of covered electrode or welding torch and the angle of resultant force can be changed. Changing the way and speed of bar conveying can effectively control the temperature of the molten pool and prevent the molten pool from falling due to gravity. Therefore, short arc operation is advocated, firstly, to reduce heat radiation loss; The second is to effectively overcome the role of gravity.

(2) Control and treatment of welding deformation It is difficult to control welding deformation because objects have the characteristics of thermal shrinkage and cold shrinkage. The key is to control the internal stress of the weld or exert a reaction force on the internal stress. The purpose of adopting reserved reverse deformation, reasonable welding sequence or rapid cooling is to control the internal stress from being too large; Rigid fixation is pre-tension; When correcting deformation, local heating, mechanical jacking and hammering are all reaction forces to apply internal stress.

3. Chemistry:

(1) Be familiar with the periodic table of elements, have a certain understanding of the main elements of various commonly used materials, and have a certain understanding of the content ratio of harmful elements and beneficial elements. When choosing welding materials, we can simply compare the main components of welding materials and parent materials, and determine the welding materials according to the principle of matching.

(2) In fusion welding, we should know a series of chemical reactions among molten metal, slag and gas in the welding zone at high temperature, which directly affect the composition, microstructure and properties of weld metal. During the welding process, O2, H2 and N2 have great influence on the weld quality. They come from air, coating or flux, and impurities on the weld, such as the reaction of O2 with C or H2, and the CO gas or H2O produced is no deeper than metal. If it cannot escape smoothly, it will form pores. H2 porosity is the most harmful, which mainly comes from the decomposition of water at high temperature and is the main reason for the formation of cold cracks. Therefore, it is very important to bake the welding material before welding and clean the area to be welded, so as to effectively control the gas generation source; In addition, the bad weather environment (excessive wind speed and high air relative temperature) is also the main reason for porosity. Deoxidation, desulfurization, dephosphorization and alloy infiltration of slag in molten pool can effectively improve weld quality.

Segregation of weld pool after primary crystallization leads to uneven chemical composition, which is also one of the main reasons for hot cracks, slag inclusion and porosity in weld. If preheating before welding or large heat input is adopted, it can be effectively improved. In the process of secondary crystallization, the faster the cooling rate, the less ferrite precipitation and the more pearlite precipitation. By controlling the cooling rate, the ideal ferrite+pearlite structure can be obtained. Improving secondary structure is an important way to improve weld quality. Generally, multi-layer and multi-pass welding and post-weld heat treatment can be used.

The general principles of stainless steel welding are: low current, narrow weld bead and fast linear welding. In short, it is necessary to control the heat input not to be too large. Many professional books generally explain that it is to prevent alloy elements from burning. In fact, at high temperature, C+Cr=CrC. Once w(Cr) is lower than 12%, the weld may rust.

Understand some chemical characteristics of media in containers or pipelines, such as methanol, hydrogen, sulfuric acid, benzene and gasoline, which are flammable, explosive, toxic and volatile respectively, and are harmful to the environment. During such welding, no negligence is allowed, thus greatly improving the welder's quality consciousness and sense of responsibility.

4. Basic knowledge of microcomputer and related professional English vocabulary: With the continuous development of automatic numerical control technology, welding equipment is updated faster and faster, and its professionalism and functionality are becoming stronger and stronger. Many devices are designed with operating procedures, and some welding machines have dozens of light buttons on the operation panel. How to match various parameters reasonably needs the welder to learn and understand. In addition, foreign advanced welding equipment occupies a large share in the China market, and many instructions on the LCD screen and operation keys are in English, such as AC (alternating current), DC (direct current), POWER (power supply), ON/OFF (on/off), SELECT (selection), CHANCE (change) and other professional terms and operation terms, which need to be mastered.